The invention is in the field of lamps and other devices having current lead-in conductors sealed in and through a bulb or envelope by means of current-conductive foil members.
U.S. Pat. No. 3,685,880 to John C. Sobieski, for example, discloses a lamp containing a pair of electrodes each connected to a separate lead-in conductor by a thin metal foil member, the foil members being hermetically sealed in the lamp envelope at seal regions, the end regions of the electrodes and lead-in conductors being embedded in the seal regions. The electrodes and lead-in conductors are attached to the respective foil members by positioning their end regions to overlap regions of the foil member, and spot welding these overlapped regions together. Typically, the lead-in conductors and the foil members are made of molybdenum, and, in an arc lamp, the electrodes are tungsten rods. To improve the spot-welded connections, both electrically and mechanically, small platinum-coated molybdenum foil pads have been placed at the spot-weld locations, between the molybdenum seal foil member and the tungsten electrodes and/or the molybdenum lead-in conductors, prior to spot welding. The improvement thus achieved is relatively greater for the welds of the foil member to the tungsten electrode rods. However, it has been found that this improvement in weld bonding is accompanied by an increased tendency for cracking of the envelope material at the seal region.